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Soil

You have a contaminated site which you need to clean up – what soil clean up options might you consider?

Physical clean up of soils can be undertaken to remove many forms of contaminants however the relative treatment cost of doing so can be prohibitive and time consuming limiting effectiveness on sites which require immediate development. To develop most sites an integrated approach focused on minimising waste disposal and maximising re-use is key utilising a mixture of the approaches below. The use of the CL:AIRE: Definition of Waste Code of Practice provides an overarching mechanism to enable this in many circumstances through the ability to create a development specific materials management plan.

Capping

Subject to appropriate risk assessment leave contaminated soil material in situ and place an approved barrier/thickness of soil capping composed of chemically suitable material across sensitive soft landscaped areas. This may include a capillary break layer where an engineered cap is required.

Excavation and disposal to offsite landfill

Historically and to a significant degree still currently off site disposal of soil to landfill is a common means by which to achieve this where potential site redevelopment is heavily dictated by cost, time and maximising cash flow. This reflects that whilst it is expensive it is quick and delivers a high confidence of success.

Segregation and Screening

Where mixed made ground is present this approach can be used as part of the waste minimisation process to separate materials with differing physical characteristics. This can often be successful in separating mixed materials where contamination is concentrated in one particular material type. This assists in the process of determining the ultimate end point for the waste and deciding for example based upon the volumes delivered whether or not there is sufficient scope to reuse in areas where it is safe to do so.

Bio-remediation

Where hydrocarbon (TPH) impacted soils are present with sufficient space and time this process can be used to reduce elevated TPH concentrations therein through use of existing or enhancement of natural microbial breakdown processes to deliver a soil suitable for potential re-use. Bioremediation techniques are destruction or transformation techniques directed toward stimulating the microorganisms to grow and use the contaminants as a food and energy source by creating a favorable environment for the microorganisms. Generally, this means providing some combination of oxygen, nutrients, and moisture, and controlling the temperature and pH. In situ and ex situ methods are available – the latter tends to be used more commonly.

Stabilisation

In a similar manner to lime stabilisation to improve geotechnical soil quality the use of soil stabilisation using cement or similar based additives is intended to achieve an improvement in geotechnical soil quality whilst also locking contaminants in place to ensure that in the long term they remain stable and relatively immobile offsetting potential risks to future receptors.

Thermal Treatment

Thermal treatments offer quick cleanup times but are typically the most costly treatment group. This difference, however, is less in ex situ applications than in in situ applications. Cost is driven by energy and equipment costs and is both capital and operation and maintenance intensive.

Thermal processes use heat to increase the volatility (separation); burn, decompose, or detonate (destruction); or melt (immobilization) the contaminants. Separation technologies include thermal desorption and hot gas decontamination. Destruction technologies include incineration, open burn/open detonation, and pyrolysis. Vitrification immobilizes inorganics and destroys some organics. In situ and ex situ methods are available.

Soil Washing

This is an ex-situ soil separation processes mostly based on mineral processing techniques widely used in Northern Europe and America for the treatment of contaminated soil. Soil washing is a water-based process for scrubbing soils ex-situ to remove contaminants. The process removes contaminants from soils in one of the following two ways:

By dissolving or suspending them in the wash solution (which can be sustained by chemical manipulation of pH for a period of time); or

By concentrating them into a smaller volume of soil through particle size separation, gravity separation, and attrition scrubbing (similar to those techniques used in sand and gravel operations).

How do you make an informed choice?

Please get in contact with us and let us assist you. We don’t charge for initial advice and consultation and are happy to help. Over the past 13 years we have been successful in completing a wide range of varied and complex series of contracting works from simple excavation and disposal to more complex bio-remediation and groundwater clean up. We are completely familiar with the CL:AIRE: Definition of Waste protocols and have successfully reprofiled sites to efficiently manage and maximise the re-use of unsuitable materials which would otherwise have been disposed off site to landfill.